Blood Pressure Measurement

Sphygmomanometers

There are three types of sphygmomanometers used to measure blood pressure: mercury, aneroid, and digital.

Reading blood pressure by auscultation is considered the gold standard by the Heart, Lung and Blood Institute of the NIH.

Subject

Position: supine, seated, standing.

In seated position, the subject's arm should be flexed.

The flexed elbow should be at the level of the heart.

If the subject is anxious, wait a few minutes before taking
the pressure.

Procedures

To begin blood pressure measurement, use a properly sized blood pressure cuff. The length of the
cuff's bladder should be at least equal to 80% of the
circumference of the upper arm.

Wrap the cuff around the upper arm with the cuff's lower edge
one inch above the antecubital fossa.

Lightly press the stethoscope's bell over the brachial artery
just below the cuff's edge. Some health care workers have
difficulty using the bell in the antecubital fossa, so we suggest
using the bell or the diaphragm to measure the blood pressure.

Rapidly inflate the cuff to 180mmHg. Release air from the
cuff at a moderate rate (3mm/sec).

Listen with the stethoscope and simultaneously observe the
sphygmomanometer. The first knocking sound (Korotkoff) is the
subject's systolic pressure. When the knocking sound disappears,
that is the diastolic pressure (such as 120/80).

Record the pressure in both arms and note the difference;
also record the subject's position (supine), which arm was used,
and the cuff size (small, standard or large adult cuff).

If the subject's pressure is elevated, measure
blood pressure two additional times, waiting a few minutes between
measurements.

A BLOOD PRESSURE OF 180/120mmHg OR MORE REQUIRES IMMEDIATE
ATTENTION!

Precautions

Aneroid and digital manometers may require periodic calibration.

Use a larger cuff on obese or heavily muscled subjects.

Use a smaller cuff for pediatric patients.

For pediatric patients a lower blood pressure may indicate the
presence of hypertension.

Don't place the cuff over clothing.

Flex and support the subject's arm.

In some patients the Korotkoff sounds disappear as the systolic pressure is bled down. After an interval, the Korotkoff sounds reappear. This interval is referred to as the "auscultatory gap." This pathophysiologic occurrence can lead to a marked under-estimation of systolic pressure if the cuff pressure is not elevated enough. It is for this reason that the rapid inflation of the blood pressure cuff to 180mmHg was recommended above. The "auscultatory gap" is felt to be associated with carotid atherosclerosis and a decrease in arterial compliance in patients with increased blood pressure.